21128400 has 90 divisors (see below), whose sum is σ = 73333910. Its totient is φ = 5633280.

The previous prime is 21128381. The next prime is 21128411. The reversal of 21128400 is 482112.

It can be written as a sum of positive squares in 3 ways, for example, as 5184 + 21123216 = 72^2 + 4596^2 .

It is a tau number, because it is divible by the number of its divisors (90).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 666 + ... + 6534.

Almost surely, 2^21128400 is an apocalyptic number.

21128400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21128400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36666955).

21128400 is an abundant number, since it is smaller than the sum of its proper divisors (52205510).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21128400 is a wasteful number, since it uses less digits than its factorization.

21128400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5893 (or 5879 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21128400 is about 4596.5639340708. The cubic root of 21128400 is about 276.4535705269.

It can be divided in two parts, 21128 and 400, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21128400 in words is "twenty-one million, one hundred twenty-eight thousand, four hundred".